Include WebGL2 feature in ctx.capabilities

[vorg]

Currently e.g. ctx.capabilities.textureHalfFloat is false for WebGL2 context.

[dmnsgn]

The question is: are capabalities detecting "extension presence" or WebGL (1 or 2) "functionality".

[dmnsgn]

Note: textureFilterAnisotropic and textureFloatLinear are still extensions in WebGL2 and not enabled by default.

textureHalfFloatLinear is according to:

• https://github.com/KhronosGroup/WebGL/blob/bbd2fa41e661f6d0209222aa058e76200924a1cf/sdk/tests/conformance/extensions/oes-texture-half-float-linear.html#L29
• https://stackoverflow.com/questions/43987719/the-complete-list-of-promoted-extensions-in-webgl2

[dmnsgn]

The question is: are capabalities detecting "extension presence" or WebGL (1 or 2) "functionality".

ctx.capabilities explicit if an extension is supported, regardless of the version eg. if support was added by default in WebGL 2, capability is true.

All above fixed in v3.